FIG 6.

Nitrite release by vegetative stages of S. coelicolor A3(2) and its influence on growth of substrate mycelium on solid medium (A) as well as in liquid culture (B, C). (A) Nar-dependent nitrate reduction in germlings of the strains indicated on the right. For the determination of nitrite production (the two columns on the left), spore suspensions (5 μl of a suspension with an OD₄₅₀ of 20) were incubated aerobically for 10 h. After germination, the plates were incubated under anaerobic conditions for 3 days at 30°C. In the wells labeled NO₃⁻, 5 mM sodium nitrate was included in the medium. Colony development (the two columns on the right) was analyzed by placing spore suspensions (5 μl a suspension with an OD₄₅₀ of 1) on YEME-MOPS-agar (3 ml) and incubating the plates for 9 days aerobically with or without 50 mM nitrate. (B, C) Growth curves for the wild-type strain M145 were performed in 24-well plates in 1 ml (circles) or 2 ml (triangles) of TSB medium. The cultures whose results are shown in panel B were inoculated with spores to an OD₄₅₀ of 0.25, whereas those whose results are shown in panel C were inoculated with highly dispersed mycelium (see Materials and Methods) to 150 CAE/ml. The plates were incubated without nitrate (filled symbols), with 20 mM nitrate (open symbols) (B), or with different concentrations of nitrite (filled circles and full line, no nitrite; filled circles and dashed line, 5 mM nitrite; open circles and dashed line, 25 mM nitrite; open circles and dotted line, 50 mM) (C).